Flow cytometry of such parameters as DNA, RNA, surface and/or internal antigen and total protein content of tumor cells or nuclei is widely used in cancer research and is finding increasing clinical application. The useful information about the biology of normal and abnormal cellular development, the perturbation of cell function by therapeutic agents, and the biologic behavior of tumors in patients obtained to data from one- and two-parameter flow cytometry has led investigators to attempt more sophisticated studies in which DNA, RNA, one or more cellular antigens, and light scattering or extinction are measured simultaneously. We have developed the multiple beam apparatus and many of the staining procedures usable for such analyses; however, the techniques have remained inaccessible to many investigators because of the difficulty and cost of implementing them on conventional commercial flow cytometers. The present study will examine the performance of two newer flow cytometers using low-power laser light sources in multiparameter analysis of DNA, RNA, and immunofluorescence and/or protein content in cells derived from human tumors. These instruments, potentially much more affordable and easier to use than existing systems, could make it possible for many more laboratories to pursue clinical and experimental applications of multiparameter flow cytometry.